Peel and stick decoupling membrane

ABSTRACT

An automated method of manufacturing a decoupling underlayment membrane is provided, the method retrieving a membrane sheet, thermoforming a set of cavities into a top surface of the membrane sheet and pressing a set of through holes into the membrane sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/949,762, filed Nov. 23, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/046,885, filed Oct. 4, 2013, now issued as U.S.Pat. No. 9,194,119, which claims the benefit of U.S. ProvisionalApplication No. 61/709,984, filed Oct. 4, 2012, and U.S. ProvisionalApplication No. 61/869,636, filed Aug. 23, 2013, all of which areincorporated herein by reference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

Conventional underlayment membranes use so-called “dovetail” cavitiessituated in longitudinal and transverse directions to decrement stressexerted on the external surface of installed flooring tiles, and usegrooves formed in longitudinal and transverse directions behind“dovetail” cavities to channel water (such as moisture and vapor) abovea subfloor. Additionally, conventional underlayment membranes requirefine-mesh screen fabric webbings attached to the underside of themembranes to anchor mortar so that the membranes can be adhered to thesubfloor with interlocked mortar formed on the webbings.

These characteristics of conventional underlayment membranes result inseveral disadvantages. First, the “dovetail” cavities, which haveoverhangs and undercuts, cause the manufacturing of the membranes to bequite expensive, since specially made machines must be used for themanufacturing. Second, a flooring installer has to apply mortar onto theunderside webbings for the webbings to adhere to a subfloor in order toinstall flooring tiles on the membranes, which is inconvenient andincurs additional installation cost. Third, grooves are formed inlongitudinal and transverse directions, although forming channels forwater, are still fairly restrictive, as water channeling is restrictedto be only along longitudinal and transverse directions.

In addition, the presence of perpendicular grooves may limit thestructural integrity of the membrane in such a way that cracks or otherdefects form along the grooves due to a lack of support from themembrane.

Therefore, there is a need for a self-adhesive decoupling underlaymentmembrane with a set of water displacement channels that is able toprovide appropriate support for flooring or other finished surfaces(e.g., walls, ceilings, etc.).

BRIEF SUMMARY OF THE TECHNOLOGY

Some embodiments provide a decoupling underlayment membrane that may beused during installation of flooring such as ceramic tile flooring. Theunderlayment membrane may include a set of cavities formed into the topsurface of the membrane such that thin set mortar may be applied to thetop of the membrane in order to adhere the flooring. The areassurrounding the cavities may provide a fluid pathway on the underside ofthe membrane during and after installation. The underlayment membranemay include a set of through holes, each of which allows an amount ofmortar to pass through the hole during installation such that the layerof thin set mortar is securely coupled to the underlayment (and, inturn, the subfloor).

The underlayment membrane may further include a peel and stick adhesivelayer on the bottom surface of the membrane, such that the membrane maybe adhered directly to a subfloor. The peel and stick layer may includea release liner that is removed just before installation to expose theadhesive on the bottom surface of the peel and stick layer.

A first exemplary embodiment of the invention provides a decouplingunderlayment membrane. The decoupling underlayment membrane includes: aset of mortar cavities; a set of through holes; and an adhesive layercoupled to an exterior surface of each mortar cavity in the set ofcavities.

A second exemplary embodiment of the invention provides a method ofmanufacturing a decoupling underlayment membrane. The method includes:retrieving a membrane sheet; thermoforming a set of cavities into a topsurface of the membrane sheet; pressing a set of through holes into themembrane sheet.

A third exemplary embodiment of the invention provides a decouplingunderlayment membrane. The decoupling underlayment membrane includes: aset of starfish-shaped cavities arranged in a first repeating patternand formed into a top surface of the membrane; a set of through holesarranged in a second repeating pattern; and a peel and stick adhesivelayer coupled to a bottom surface of the membrane.

The preceding Summary is intended to serve as a brief introduction tovarious features of some exemplary embodiments of the invention. Otherembodiments may be implemented in other specific forms without departingfrom the spirit of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of theinvention are set forth in the following drawings.

FIG. 1 illustrates a top view of a decoupling membrane according to anexemplary embodiment of the invention;

FIG. 2 illustrates a close-up top view of a portion of the decouplingmembrane of FIG. 1;

FIG. 3 illustrates a perspective cross-section view of the decouplingmembrane of FIG. 1;

FIG. 4 illustrates an alternative perspective cross-section view of thedecoupling membrane of FIG. 1;

FIG. 5 illustrates a bottom perspective view of the decoupling membraneof FIG. 1;

FIG. 6 illustrates a top perspective view of the decoupling membrane ofFIG. 1;

FIG. 7 illustrates a bottom perspective view of the decoupling membraneof FIG. 1 as installed;

FIG. 8 illustrates an exploded bottom perspective view of the decouplingmembrane of FIG. 1 as installed;

FIG. 9 illustrates a side view of the decoupling membrane of FIG. 1 asinstalled;

FIG. 10 illustrates an alternative side view of the decoupling membraneof FIG. 1 as installed;

FIG. 11 illustrates a top view of an alternative decoupling membraneaccording to an exemplary embodiment of the invention; and

FIG. 12 illustrates a flow chart of a conceptual manufacturing processused by some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out exemplary embodiments of the invention. Thedescription is not to be taken in a limiting sense, but is made merelyfor the purpose of illustrating the general principles of the invention,as the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.Broadly, embodiments of the present invention generally provide anunderlayment membrane used for installing flooring on subfloor (e.g.,concrete, wood slab, etc.). The membrane may be a peel-and-stickunderlayment membrane that effectively decouples the flooring undersidesurface from the subfloor so as to achieve superior stress-decouplingand decrementing and water-channeling, as well as numerous otheradvantages.

FIG. 1 illustrates a top view of a decoupling membrane 100 according toan exemplary embodiment of the invention. As shown, the decouplingmembrane may include multiple cavities 110 spread through the membrane100 using various appropriate layouts (e.g., staggered, interlocking,etc.). In some embodiments, each of the cavities 110 may be shaped as afive-pronged “star”. Such a cavity shape may allow for interlocking (ornearly interlocking) layouts that allow water or other fluid to passthrough channels formed among the spaces between the cavities, thusallowing for improved drainage. Different embodiments may includedifferent cavity shapes.

The cavities may be sized appropriately for different types of mortarthat may be associated with different types of flooring or differentinstallation locations (and/or other appropriate factors). For instance,in some embodiments, each cavity may be approximately three quarters ofan inch across and one quarter inch deep.

The underside, or the bottom surface, of each cavity may have a texturedsurface, such as a plastic surface having hair cell texture. Such atextured surface may improve adhesive bonding when the membrane isplaced against a subfloor, thus allowing the entire membrane sheet to befirmly adhered to the sub floor without any need to apply mortar (and/orother materials) to the bottom surface of the membrane.

The bottom surface of the cavities may be covered by a release liner(not shown) that forms a peel-and-stick layer.

Situated among the cavities are multiple “punch” holes 120, which mayfunction as “escaping” holes for mortar (e.g., thin-set mortar) appliedon the top plane of the membrane 100. The holes 120 may be sizedappropriately (e.g., one-eight inch diameter) such that an appropriateamount of mortar is able to pass through the hole (i.e., enough mortarto form a bond, but not so much mortar that the drainage pathways areblocked).

In some embodiments, the membrane 100 may be made from polyvinylchloride (PVC). Such a membrane may be provided in semi-rigid sections(e.g., eighteen inch by twenty-four inch sections of twenty-six mil PVC,where the sections may be made from a bisected forty inch by forth-eightinch thermoformed panel, one-foot square sections, etc.). Alternatively,the membrane may be provided as a roll, where an appropriate width(e.g., twenty-four inches) and length of membrane may be wrapped about acylindrical core allowing installation across larger areas.

The membrane 100 may be formed in some embodiments by taking a sheet ofmaterial (e.g., twenty inches by twenty-six inches) and pressing arepeating pattern onto the sheet using a thermoforming tool (e.g., bypressing a heated die into the sheet). Such a pattern may repeat atvarious appropriate intervals (e.g., a one inch horizontal interval anda one inch vertical interval). The sheet may then be trimmed to a finalsize. Alternatively, a pattern may be repeatedly formed into a length offlexible material and the material may be rolled about a core. Inaddition, an adhesive layer may be applied to the bottom surface of themembrane. The adhesive layer may include a release liner that may beremoved prior to installation to expose the adhesive layer.

During installation of flooring tiles (such as ceramic tiles), and/orother types of flooring or finish materials, the cavities 110 (openingto the top plane of the membrane) may be filled with mortar as mortar isapplied to the top side surface of the membrane 100, thus allowing theflooring to be firmly adhered to the top surface of the membrane. Afterinstallation, when stress is exerted on the top surface of the installedflooring, mortar is pushed through the holes 120 to form attachmentfeatures (or “rivet heads”) on the underside of the membrane. Such anarrangement may effectively decrement stress.

One of ordinary skill in the art will recognize that the membrane 100may be implemented in various different ways without departing from thespirit of the invention. For instance, different embodiments may includecavities of different shape, size, position, and/or other differences.In addition, the membrane itself may be provided in various differentways (e.g., sheets of different size and/or shape, membranes ofdifferent thicknesses, etc.).

FIG. 2 illustrates a close-up top view of a portion 200 of thedecoupling membrane 100 FIG. 3 illustrates a perspective cross-sectionview of the decoupling membrane 100 along line 9-9 of FIG. 2. As shown,the cavities 110 open to the top surface of the decoupling membrane 100such that mortar applied to the top surface will fill the cavities. FIG.4 illustrates an alternative perspective cross-section view of thedecoupling membrane 100 along line 8-8 of FIG. 2.

FIG. 5 illustrates a bottom perspective view of the decoupling membrane100. This figure highlights the underside surface of the membranecavities, which may be a textured surface adapted to enhance adhesionbetween the underside surface and the subfloor. FIG. 6 illustrates a topperspective view of the decoupling membrane 100.

FIG. 7 illustrates a bottom perspective view of the decoupling membrane100 as installed. In this figure, the subfloor and adhesive layer areomitted for clarity. As shown, the installation 700 includes a flooringlayer 710, a mortar layer 720, the membrane 100, and a set of rivetheads 730. The rivet heads may be formed as the mortar passes throughescaping holes in the membrane 100. Such rivet heads 730 may help securethe mortar and flooring to the membrane 100. In addition, the escapingholes may be sized such that the rivet heads 730 do not completely blockthe drainage channels formed among the filled cavities.

FIG. 8 illustrates an exploded bottom perspective view of the decouplingmembrane 100 as installed. As shown, the installation 800 includes theinstallation 700 described above in reference to FIG. 7. In addition,installation 800 shows a peel and stick layer 810 and a subfloor 820.The subfloor may be any appropriate material (e.g., plywood, concrete,etc.).

The peel and stick layer 810 in this example includes a first releaseliner 830 and a second release liner 840. The first release liner 830may typically be removed when manufacturing the membrane such that thelayer 810 may be attached to the bottom surface of the membrane 100.Alternatively, an adhesive may be applied to the layer 810 (and/or thebottom surface of the membrane 100) and the layer 810 adhered to thebottom surface of the membrane 810 without use of the first releaseliner. The second release liner 840 may be removed just prior toattaching the membrane 100 to the subfloor 820. In some embodiments, thelayer 810 may include a carrier which has adhesive on both sides(covered by the release liners 830-840).

In some embodiments, one or both release liners 830-840 may be dividedinto multiple sections for each section of membrane 100. Such “split”release liners may allow an installer to more easily remove the liner(especially from the non-flat bottom surface of the membrane). Someembodiments may include an attached tab or other graspable portionattached to the liner such that an installer may easily peel away theliner.

FIG. 9 illustrates a side view of the decoupling membrane 100 asinstalled. FIG. 10 illustrates an alternative side view of thedecoupling membrane 100 as installed.

The advantages of a decoupling membrane as described above are numerous.A peel-and-stick membrane (incorporating, for example, pressuresensitive acrylic (PSA) or rubber based adhesive affixed to bottomplates of cavities and release liner sheet) enables dramaticallyquicker, easier installation of the membrane directly to a subfloor.

The peel and stick three-part layer created via paper release linerbeing peeled away from the adhesive and adhesive carrier (which remainintact across the bottom plane of the membrane), as affixed to thecollective bottom planes of each cavity, enables the membrane to beadhered to the subfloor as one uniform element. This yields a vastlysuperior and installer-friendly product as opposed to continuous rollmembranes that require adhesive mortar to be applied to and penetratedinto fine-mesh screen fabric webbing (attached to the underside of themembrane) to become interlocked in the webbing so as to anchor themembrane to a subfloor, as is the case for the conventional membranes.

Tenacious bond strength is enabled between flooring tiles (such asceramic tiles) and the membrane via the mortar-penetrating punch holes.After peel-and-stick installation of a disclosed membrane to a subfloor,in preparing to install ceramic tiles, mortar is spread across surfaceof the disclosed membrane. Mortar both fills cavities and penetrates andperforates through the holes located across the top plane of thedisclosed membrane and placed between the cavities. Mortar protrudesthrough holes in the top surface, then expands below around underside ofthe surface edge of the holes and creates expanded heads of mortar onunderside of the top surface, similar to a rivet head. The mortar thencures, leaving a securing rivet head on the underside and preventing themortar/tile assembly from separating from the membrane. These punchholes effectively decrement the stress difference and lateral tensionacross the surface layer of the membrane.

The exemplary five-pronged star-shaped cavity design maximizes cavitywall surface area to which mortar cement affixes during ceramic tileinstallation process. By incorporating these five decagon-angledprotuberances, the spread-out star configuration (or other similarconfigurations) facilitates a greatly increase total cavity inside wallsurface area as compared to square or rectangular cavities. Suchincreased surface area provides more surface area extant for mortar toaffix, thus strengthening the flooring bond to the decoupling membrane.

Each cavity wall may be perpendicular to the bottom surface of eachcavity. By squaring off the interior of each cavity at the inside walland base of each cavity, the bottom underside surface area (on eachcavity onto which peel-and-stick adhesive may adhere) is effectivelymaximized. This allows more contiguous surface area on the bottom ofeach cavity onto which the applied PSA and accompanying release linerare able to adhere.

The textured underside bottom surface plane of each cavity creates amore dynamic surface and maximizes gripping engagement between theadhesive carrier and cavity bottom. This in turn creates strongeradhesive bonds between a subfloor and the bottom of each cavity andbetween a subfloor and the underside of a disclosed membrane as whole.

The offset interlocking pattern of channels between the star shapedcavity pockets allows for vapor equalization and allow for the membraneto be able to be installed over, for instance, incompletely curedconcrete. In some embodiments, the adhesive layer on the bottom of themembrane may include perforations that allow moisture to pass throughthe adhesive layer (which may include a carrier or substrate layer thatthe adhesive adheres to) and reach the channels. Such perforations maybe evenly spaced throughout the layer (e.g., every one quarter inch) andmay be sized appropriately for the subfloor material type.

The vertical inside slope of each cavity enables easy fabrication andfacilitates easy removal of the membrane from a mold, thus enabling easyworkability from mold into volume production. Alternatively, themembrane may be formed by pressing a die into a sheet of material, wherethe vertical slope allows the die to be pressed directly perpendicularto the sheet. This design facilitates a straightforward mold releaseprocess, and enables disclosed membranes to bypass mold release issueswhile maintaining substantial surface area both to facilitate mortaradhesion and accommodate lateral tension. As a skilled artisan readilyappreciates, this is a significant manufacturing and productionadvantage over membrane designs utilizing cavities with so-calleddove-tail negative angle cut backs, wherein specifically proprietary orpatented equipment (e.g., a large cylindrical drum, gas propulsionextraction equipment, etc.) is required to both mold and extractmembranes.

FIG. 11 illustrates a top view of an alternative decoupling membrane1100 according to an exemplary embodiment of the invention. Decouplingmembrane 1100 may be substantially similar to decoupling membrane 100,with different cavities 1110 (and/or a different arrangement ofcavities) and through-holes 1120 than those described above in referenceto membrane 100.

This inter-locking (or “inter-leaving”) pattern of cavities 1110 helpsmaximize the total available adhesion surface on the bottom of themembrane 1100, to which the self-adhering adhesive (e.g., an acrylic orrubberized adhesive), adhesive-bearing “carrier” (e.g., polyester) andrelease liner (either silicone treated paper or a thin plastic film)layer will adhere, thus allowing “peel-and-stick” installation.

The through holes 1120, which may be formed in various appropriate ways(e.g., using a set of hole punches), facilitate the penetration of thinset mortar (or “thin set”) during flooring installation, which thencures onto the underside of the top of the membrane 1100 into a patternof anchoring rivet head fasteners, augmenting the separate thin setmortar bonding created by the embedding and curing of mortar into thestarfish cavities 1110 on the top side of the membrane 1100.

As shown, in this example, each row of cavities 1110 is rotated onehundred eighty degrees from the adjacent rows of cavities. Such aconfiguration may allow the cavities to be placed in an overlapping (ornearly overlapping) arrangement that may maximize the surface areaprovided by the cavities (and thus maximize the surface area that isavailable to adhere to a subfloor, and, of course, provide support tothe installed flooring or other finish layer) while still allowing avapor channel formed by the spaces between the cavities on the undersideof the installed membrane 1100.

The layout of cavities 1110 and holes 1120 may be associated with a setof X and Y axis lines 1130. For instance, in this example, a grouping1140 of cavities and holes may be repeatedly stepped across the membrane1100 to generate the desired overall layout.

The membranes of some embodiments may be manufactured at least partlyusing thermoforming, where a plastic sheet is heated to a pliableforming temperature, formed to a specific shape using a mold or die, andtrimmed to create a usable product. The sheet, or “film” when referringto thinner gauges and certain material types (such as PVC), may beheated in an oven to a high-enough temperature that the sheet may bestretched into or onto a mold (or a mold may be pressed into or onto thesheet) and cooled to a finished shape.

FIG. 12 illustrates a flow chart of a conceptual manufacturing process1200 used by some embodiments. Such a process may be implemented usingautomated equipment (e.g., computer-controlled handlers, machines,etc.).

As shown, the process may retrieve (at 1210) a membrane sheet (e.g., asheet of PVC). The process may then thermoform (at 1220) cavities in themembrane. Such cavities may alternatively be formed in other ways (e.g.,using a mold).

Process 1200 may then press (at 1230) holes in the membrane (and/orotherwise form appropriate through holes). The process may then apply(at 1240) an adhesive layer to the membrane. Before application, theadhesive layer may be perforated using appropriate tooling (e.g., a setof punches of appropriate size) to allow moisture to pass through thelayer. Next the process may trim (at 1250) the membrane sheet to thefinal size. The process may then determine (at 1260) whether themembrane is a rolled product. If the process determines that themembrane is not a rolled product, the process may end. If the processdetermines that the product is rolled, the process may wrap (at 1270) alength of the membrane about a core.

One of ordinary skill in the art will recognize that process 1200 isconceptual in nature and may be implemented in various ways withoutdeparting from the spirit of the invention. For instance, the operationsmay be performed in a different order. As another example, variousadditional operations may be included and/or listed operations omitted.The process may be implemented as part of a larger macro-process, ordivided into a set of sub-processes.

The membrane of some embodiments, by avoiding overhangs and undercutssuch as those embodied in existing membranes, can advantageously reducemanufacturing cost. The disclosed design reduces manufacturing costwhile maintaining the functionalities of smoothing out stressdifferences, facilitating peel-and-stick installation and providing achannel for fluid to escape.

The membrane manufacturing process may utilize, for instance, a smalltabletop (e.g., forty inches by forty-eight inches, forty inches byforty-four inches, etc.) machine, which may be used to heat small cutsections of plastic sheet and stretch the heated sheet over a mold usingvacuum. A peel-and-stick adhesive layer may be applied to the bottomsurface of the membrane. As above, some embodiments may provide a lengthof material on a flexible material that is able to be rolled about acore for ease of use during installation of flooring.

Other more complicated and cost-intensive thermoforming processesrequired by existing designs may involve wrapping a mold around a large(e.g., nine foot length) cylindrical drum. After a short form cycle, aburst of reverse air pressure is actuated from the vacuum side of themold as the form tooling opens, commonly referred to as air-eject, tobreak the vacuum and assist the formed parts off of, or out of, themold. A stripper plate may also be utilized on the mold as it opens forejection of more detailed parts or those with negative-draft, undercutareas. The sheet containing the formed parts then indexes into a trimstation on the same machine, where a die cuts the parts from theremaining sheet web, or indexes into a separate trim press where theformed parts are trimmed.

During installation of existing membranes, an installer is required tomix and lay down a bed (e.g., three-eighths of an inch) of thin setmortar, then roll out and embed the membrane mat into the wet mortar,working around/through the already-laid bed of mortar on the floor whilelaying down adjacent sections of mat, then wait overnight for the thinset to cure before beginning the tiling job (or other flooring or finishmaterial installation) the following day.

Conversely, the peel and stick configuration of some embodiments mayallow an installer to simply remove the release liner, press thedecoupling membrane onto the subfloor and immediately begin a tilingproject (or other finish project). This configuration results in athinner profile, no downtime waiting for thin set to cure, and noadditionally required setting materials. The installer may peel eachpanel (or sheet, rolled section, etc.) and lay the membrane downadjacent to a previously laid section.

The punch holes of some embodiments may be created using a tooling diewhich may be essentially a mounted series of awls, which, when heated,are depressed into the appropriate locations on top surface of top layerof the membrane. The depth to which the awls pierce the membrane maycorrespond to the diameter of the awls and thus determine the diameterof the punch holes (which results in appropriately sized rivet headswhen thin set is applied to the top of the membrane).

The alternating rotating starfish design of some embodiments may allowintersecting X and Y axis lines delineating each grouping of fourcavities (and/or other appropriate groupings). By rotating the angle ofeach starfish cavity within alternating rows, the design enables thedistal end points of respective adjacent cavities to abut against acommon imaginary grid line touched on also by distal ends of opposingcavities (i.e., nearly overlapping, or separated by a small distance).

Thus, each respective cavity may be touching and essentially sharing thesame X and Y axis grid lines, via two or three extended “arms”, with twoor three extended arms from adjacent cavities, depending on the cavityposition within the grid.

By alternately balancing the positioning relationship of the respectivecavities, and maintaining each of their outward-facing (from withintheir grid) arms abutting to the common X or Y axis, the alternatingrotating starfish design may effectively maintain a consistent uniformspacing between every cavity arm throughout the entire membrane,accompanied by consistent uniform interceding bridge strength throughoutthe entire membrane.

Each grouping of cavities may be defined as a square, with punch holeslocated along the edges of the square (and falling on the X and Y axisgrid lines in some embodiments). Such groupings may maintain a uniformbridge wall between the cavities and punch holes. Such an approachmaintains a uniform structural integrity of the entire membrane whileaffording distinct recesses and ports for thin set mortar adhesion andpenetration on the top of the membrane and maximum possible surface areafor adhesive layer adhesion on the bottom of the membrane.

Some PVC-based embodiments of the membrane may include anti-dioxins toprevent the membrane from rotting.

After removing each PVC membrane from the mold, perforating the membranewith punch holes, and allowing the membrane to cool, the bottom surfaceof the membrane may be contacted by an abrasive rigid surface, such thata sufficient portion of the bottom surface plane is abraded (or“scuffed”). This surface-roughing preparation (priming) step creates amore receptive surface onto which the peel and stick layer may beadhered.

It should be understood, of course, that the foregoing relates toillustrative details of exemplary embodiments of the invention and thatmodifications may be made without departing from the spirit and scope ofthe invention as defined by the following claims.

We claim:
 1. An automated method of manufacturing a decouplingunderlayment membrane, the method comprising: retrieving a membranesheet; thermoforming a set of cavities into a top surface of themembrane sheet; and pressing a set of through holes into the membranesheet.
 2. The method of claim 1, further comprising applying a peel andstick adhesive layer to a bottom surface of the membrane sheet.
 3. Themethod of claim 1, wherein each cavity in the set of cavities has astar-like shape.
 4. The method of claim 1, wherein thermoforming the setof cavities comprises: heating the membrane sheet; and pressing a dieinto the membrane sheet to form the cavities.
 5. The method of claim 4,wherein the die has a cavity layout that includes a grouping of fourcavities repeated across the die.
 6. The method of claim 1, whereinpressing a set of through holes comprises: heating the membrane sheet;and pressing a set of awls into the membrane sheet to form the throughholes.
 7. The method of claim 6, wherein the size of each through holeis at least partly determined by a depth the set of awls is pressed intothe sheet.